Lossless variable transmission reflection switch controlled by the phase of a microwave drive

ABSTRACT

A technique relates to a microwave switch. A first nondegenerate device includes a first port and a second port. A second nondegenerate device includes another first port and another second port, the second port being coupled to the another second port, where the first nondegenerate device and the second nondegenerate device are configured to receive a phase difference in microwave drives. A first input/output port is coupled to the first port and the another first port. A second input/output port is coupled to the first port and the another first port, where communication between the first input/output port and the second input/output port is based on the phase difference.

BACKGROUND

The present invention generally relates to superconducting devices, andmore specifically, to a microwave switch such as a lossless, variabletransmission-reflection switch that is fully controlled by the phase ofa microwave drive.

A microwave switch or radio frequency switch is a device to route highfrequency signals through transmission paths. RF and microwave switchesare used extensively in microwave test systems for signal routingbetween instruments and devices under test (DUT). Incorporating a switchinto a switch matrix system enables the system to route signals frommultiple instruments to single or multiple DUTs. This allows multipletests to be performed with the same setup, thus eliminating the need forfrequent connects and disconnects. The entire testing process can beautomated, which increases system throughput in high-volume productionenvironments. Like other electrical switches, RF and microwave switchesprovide different configurations for many different applications.

Superconducting quantum computing is an implementation of a quantumcomputer in superconducting electronic circuits. Quantum computationstudies the application of quantum phenomena for information processingand communication. Various models of quantum computation exist, and themost popular models incorporate the concepts of qubits and quantumgates. A qubit is a generalization of a bit that has two possiblestates, but can be in a quantum superposition of both states. A quantumgate is a generalization of a logic gate, however the quantum gatedescribes the transformation that one or more qubits will experienceafter the gate is applied on them, given their initial state.

The electromagnetic energy associated with the qubit can be stored inso-called Josephson junctions and in the capacitive and inductiveelements that are used to form the qubit. In one example, to read outthe qubit state, a microwave signal is applied to the microwave readoutcavity that couples to the qubit at the cavity frequency. Thetransmitted (or reflected) microwave signal goes through multiplethermal isolation stages and low-noise amplifiers that are required toblock or reduce the noise and improve the signal-to-noise ratio. Themicrowave signal is measured at room temperature. The amplitude and/orphase of the returned/output microwave signal carry information aboutthe qubit state, such as whether the qubit is at the ground or excitedstates or at a superposition of the two states. A microwave switch canbe utilized in the communication of quantum signals associated withqubits, qubit gates, and quantum communications in general.

SUMMARY

Embodiments of the present invention are directed to a microwave switch.A non-limiting example of the microwave switch includes a firstnondegenerate device including a first port and a second port. Themicrowave switch includes a second nondegenerate device includinganother first port and another second port, the second port beingcoupled to the another second port, wherein the first nondegeneratedevice and the second nondegenerate device are configured to receive aphase difference in microwave drives. The microwave switch includes afirst input/output port coupled to the first port and the another firstport and a second input/output port coupled to the first port and theanother first port, wherein communication between the first input/outputport and the second input/output port is based on the phase difference.

Embodiments of the present invention are directed to a method ofconfiguring a microwave switch. A non-limiting example of the methodincludes providing a first nondegenerate device including a first portand a second port and a second nondegenerate device comprising anotherfirst port and another second port, the second port being coupled to theanother second port, where the first nondegenerate device and the secondnondegenerate device are configured to receive a phase difference inmicrowave drives. The method includes coupling a first input/output portto the first port and the another first port and coupling a secondinput/output port to the first port and the another first port, whereincommunication between the first input/output port and the secondinput/output port is based on the phase difference.

Embodiments of the present invention are directed to a microwave switch.A non-limiting example of the microwave switch includes a firstJosephson parametric converter comprising a Signal port and an Idlerport and a second Josephson parametric converter comprising anotherSignal port and another Idler port, the Signal port and the anotherSignal port being coupled together, where the first and second Josephsonparametric converters are configured to receive a phase difference inmicrowave drives. The microwave switch includes a first input/outputport and a second input/output port coupled to the Signal port and theanother Signal port, such that communication between the Signal andanother Signal ports is based on the phase difference.

Embodiments of the present invention are directed to a method ofconfiguring a microwave switch. A non-limiting example of the methodincludes providing a first Josephson parametric converter comprising aSignal port and an Idler port and a second Josephson parametricconverter comprising another Signal port and another Idler port. Themethod includes coupling the Signal port to the another Signal port,wherein the first and second Josephson parametric converters areconfigured to receive a phase difference in microwave drives. Also, themethod includes coupling a first input/output port and a secondinput/output port to the Signal port and the another Signal port, suchthat communication between the first and second input/output ports isbased on the phase difference.

Embodiments of the present invention are directed to a method ofoperating a microwave switch. A non-limiting example of the methodincludes receiving, by the microwave switch, a signal at one of a firstinput/output port and a second input/output port. The method includesreceiving, by the microwave switch, pump signals having a phasedifference and controlling communication of the signal between the firstinput/output port and the second input/output port based on the phasedifference.

Additional technical features and benefits are realized through thetechniques of the present invention. Embodiments and aspects of theinvention are described in detail herein and are considered a part ofthe claimed subject matter. For a better understanding, refer to thedetailed description and to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The specifics of the exclusive rights described herein are particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features and advantages ofthe embodiments of the invention are apparent from the followingdetailed description taken in conjunction with the accompanying drawingsin which:

FIG. 1 depicts a two-port microwave switch as an open switch accordingto embodiments of the present invention;

FIG. 2 depicts the two-port microwave switch as a closed switchaccording to embodiments of the present invention;

FIG. 3 depicts a signal flow graph for a nondegenerate three-wave mixingdevice in frequency conversion according to embodiments of the presentinvention;

FIG. 4 depicts a lossless or superconducting variable-transmissiontwo-port microwave switch according to embodiments of the presentinvention;

FIG. 5 depicts a lossless variable-transmission two-port microwaveswitch according to embodiments of the present invention;

FIG. 6 depicts a lossless variable-transmission two-port microwaveswitch with a modification to how the pump signal is fed according toembodiments of the present invention;

FIG. 7 depicts a lossless variable-transmission two-port microwaveswitch according to embodiments of the present invention;

FIG. 8 depicts a lossless variable-transmission two-port microwaveswitch with a modification to how the pump signal is fed according toembodiments of the present invention;

FIG. 9 depicts a signal flow graph of the lossless variable-transmissiontwo-port microwave switch according to embodiments of the presentinvention;

FIG. 10A depicts an example of the microwave switch at a working pointaccording to embodiments of the present invention;

FIG. 10B depicts an example of the microwave switch at the same workingpoint in FIG. 10A but with a different phase difference according toembodiments of the present invention;

FIG. 11A depicts an example of the microwave switch at a working pointaccording to embodiments of the present invention;

FIG. 11B depicts an example of the microwave switch at the same workingpoint in FIG. 11A but with a different phase difference according toembodiments of the present invention;

FIG. 12A depicts path 1 of the microwave switch for S₂₁ according toembodiments of the present invention;

FIG. 12B depicts path 2 of the microwave switch for S₂₁ according toembodiments of the present invention;

FIG. 12C depicts path 3 of the microwave switch for S₂₁ according toembodiments of the present invention;

FIG. 12D depicts path 4 of the microwave switch for S₂₁ according toembodiments of the present invention;

FIG. 13A depicts path 1 of the microwave switch for S₂₂ according toembodiments of the present invention;

FIG. 13B depicts path 2 of the microwave switch for S₂₂ according toembodiments of the present invention;

FIG. 13C depicts path 3 of the microwave switch for S₂₂ according toembodiments of the present invention;

FIG. 13D depicts path 4 of the microwave switch for S₂₂ according toembodiments of the present invention;

FIG. 14 depicts a table of the five operational modes of the microwaveswitch according to embodiments of the present invention;

FIG. 15 depicts an example of the microwave switch without illustratingthe hybrid coupler according to embodiments of the present invention;

FIG. 16 depicts an example of the microwave switch without illustratingthe hybrid coupler according to embodiments of the present invention;

FIG. 17 depicts a partial view of the microwave switch illustratingconnection of the resonators to the hybrid coupler according toembodiments of the present invention;

FIG. 18 depicts a flow chart of a method of forming/configuring amicrowave switch according to embodiments of the present invention;

FIG. 19 depicts a flow chart of a method of forming/configuring amicrowave switch according to embodiments of the present invention; and

FIG. 20 depicts a flow chart of a method of operating a microwave switchaccording to embodiments of the present invention.

The diagrams depicted herein are illustrative. There can be manyvariations to the diagram or the operations described therein withoutdeparting from the spirit of the invention. For instance, the actionscan be performed in a differing order or actions can be added, deletedor modified. Also, the term “coupled” and variations thereof describeshaving a communications path between two elements and does not imply adirect connection between the elements with no interveningelements/connections between them. All of these variations areconsidered a part of the specification.

In the accompanying figures and following detailed description of thedisclosed embodiments, the various elements illustrated in the figuresare provided with two or three digit reference numbers. With minorexceptions, the leftmost digit(s) of each reference number correspond tothe figure in which its element is first illustrated.

DETAILED DESCRIPTION

For the sake of brevity, conventional techniques related tosemiconductor and/or superconducting devices and integrated circuit (IC)fabrication may or may not be described in detail herein. Moreover, thevarious tasks and process steps described herein can be incorporatedinto a more comprehensive procedure or process having additional stepsor functionality not described in detail herein. In particular, varioussteps in the manufacture of semiconductor and/or superconducting devicesand semiconductor/superconductor-based ICs are well known and so, in theinterest of brevity, many conventional steps will only be mentionedbriefly herein or will be omitted entirely without providing thewell-known process details.

Turning now to an overview of technologies that are more specificallyrelevant to aspects of the invention, as previously noted herein, amicrowave switch or radio frequency switch is a device to route highfrequency signals through transmission paths. Known microwave switchessuffer from a variety of shortcomings. For example, known microwaveswitches have less than unity transmission, are not scalable because thetransmission will drop further, and have possible parasitic couplingbetween their inputs and outputs. Other problems with known microwaveswitches include that bandwidths of the resonators and narrow-bandhybrids effectively limit the maximum bandwidth that can be achieved toapproximately 150 megahertz (MHz), having four ports but only threebeing used, and requiring critical matching between the two resonatorarms.

Turning now to an overview of the aspects of the invention, one or moreembodiments of the invention address the above-described shortcomings ofthe prior art by providing a lossless superconducting microwave switch(e.g., as depicted in FIG. 4) that can be used in routing quantum and/orcontrol signals in scalable quantum processor architectures and quantumnetworks. The lossless, superconducting microwave component can beimplemented as a microwave device such as a microwave switch. Themicrowave device/switch is configured with the following scatteringmatrix

$\lbrack S\rbrack = {\begin{pmatrix}r & t \\t^{\prime} & r\end{pmatrix} = \begin{pmatrix}{\cos\;\varphi} & {{- \sin}\;\varphi} \\{\sin\;\varphi} & {\cos\;\varphi}\end{pmatrix}}$

where φ is a phase difference of the pump drives feeding the device.This device can be used as a lossless microwave switch. It conserves thefrequency of the transmitted signal. The scattering parameters depend onthe pump phase (but not amplitude). For full range control, it issufficient to vary φ in the range from about 0 to about π/2.

Further, one or more embodiments of the invention provide a microwavedevice that realizes an on-chip two-port microwave switch (or PCBintegrated switch). The microwave device transmits or blocks (reflects)microwave signals. The microwave device supports five modes ofoperation: reflector with same phase, reflector with phase negation,reciprocal transmission, nonreciprocal transmission, and/orvariable-transmission-reflection beam-splitter. In embodiments of theinvention, the microwave device can include two nondegenerate Josephsonthree-wave mixers, one 90° hybrid coupler, and one 180° hybrid couplerfor the pump signal. Also, the microwave device (i.e., microwave switch)can include an optional phase shifter on one arm of the pump feeding thetwo three-wave mixers. The two nondegenerate three-wave mixing Josephsonelements can be coupled back-to-back with or without a delay line inbetween. The two nondegenerate three-wave mixing Josephson elementsperform upconversion/downconversion of signals in transmission. Thenondegenerate three-wave mixing devices are operated in noiselessfrequency conversion mode (i.e., no photon gain). One condition on theirworking point is that both nondegenerate three-wave mixing devices(e.g., Josephson parametric converters (JPCs)) are operated at the sameworking point, i.e., have equal reflection parameters and equalamplitude for their transmission parameter. Thus, the nondegeneratethree-wave mixing devices function as active beam splitters such thateach active beam splitter has three physically separated ports. One portsupports signals at frequency f₁. Another port supports signals atfrequency f₂. A third port allows feeding the pump drive. The pumpfrequency f_(p) is equal to the frequency difference between f₂ and f₁.Without loss of generality we assume f₂>f₁.

More specifically, the above-described aspects of the invention addressthe shortcomings of the prior art by providing and configuring themicrowave device/switch such that the phase difference between the pumpdrives feeding the two nondegenerate three-wave mixing Josephson devicesinduces a nonreciprocal phase shift to signals traversing the device.This configuration allows unity transmission and scalability. The twoports of the two active beam splitters that support signals at f₁ areconnected to a 90° hybrid coupler. The two ports of the two active beamsplitters which support signals at f₂ are connected together through adelay line in some embodiments of the invention. This shared port (e.g.,ports b1 and b2 shown in FIG. 4) supports an internal mode of thedevice, and the scheme is lossless. The lossless delay line should havean effective electrical length of multiples of pi (π) radians at thefrequency of the ports (e.g., ports b1 and b2) that are connectedtogether. The two active beam splitters are (assumed to be) nominallyidentical. The scattering parameters of the microwave device at acertain working point are determined by wave interference between 4principal paths. The scattering parameter on resonance from port i to j(where i,∈{1, 2}) vanishes if the waves that propagate from i to jinterfere destructively. The scattering parameter on resonance from porti to j (where i,∈{1, 2}) is (almost or effectively) unity if the wavesthat propagate from i to j interfere constructively. The nondegeneratethree-wave mixers can be realized using JPCs, and the bandwidth of theJPCs can be enhanced using impedance engineering of the feedlines.

Now, turning to the figures, FIG. 1 depicts a two-port microwave switchwhich is shown as an open switch according to embodiments of the presentinvention. FIG. 2 depicts the two-port microwave switch which is shownas a closed switch according to embodiments of the present invention.

In FIG. 1, the scattering matrix of an open two-port switch (up to aglobal phase) is below:

$\lbrack S\rbrack = {\begin{pmatrix}1 & 0 \\0 & 1\end{pmatrix}.}$

FIG. 1 shows waves propagating from the left side (port 1) towards theright side (port 2) but are reflected off port 1 with unity reflection.Also, FIG. 1 shows waves propagating from the right side (port 2)towards the left side (port 1) but are reflected off port 2 with unityreflection.

In FIG. 2, the scattering matrix of a closed two-port switch (up to aglobal phase) is below:

$\lbrack S\rbrack = {\begin{pmatrix}0 & i \\i & 0\end{pmatrix}.}$

FIG. 2 shows waves propagating from the left side (port 1) towards theright side (port 2) and transmitted to port 2 with unity transmission.Also, FIG. 2 shows waves propagating from the right side (port 2)towards to the left side (port 1) and transmitted to port 1 with unitytransmission.

Now, a general scattering matrix for a lossless, variable-transmissionmicrowave switch is provided below:

$\lbrack S\rbrack = \begin{pmatrix}r & t \\t^{\prime} & r\end{pmatrix}$

where |r|²+|t|²=1 and |r|²+|t′|²=1.

As an example, a microwave switch functioning as a 50:50 beam splitteris considered in which half of the signal power is reflected and half ofthe signal power is transmitted, where r=1/√{square root over (2)},|t|=1/√{square root over (2)}, and the scattering matrix is given below:

$\lbrack S\rbrack = \begin{pmatrix}\frac{1}{\sqrt{2}} & \frac{i}{\sqrt{2}} \\\frac{i}{\sqrt{2}} & \frac{1}{\sqrt{2}}\end{pmatrix}$

As another example, a microwave switch as a 25:75 beam splitter isconsidered in which one-quarter (25%) of the signal power is reflectedand three-quarters (75%) of the signal power is transmitted, where r=½,|t|=√{square root over (3)}/2, and the scattering matrix is given below:

$\lbrack S\rbrack = {\begin{pmatrix}\frac{1}{2} & \frac{i\sqrt{3}}{2} \\\frac{i\sqrt{3}}{2} & \frac{1}{2}\end{pmatrix}.}$

FIG. 3 depicts the signal flow graph for a nondegenerate three-wavemixing device operated in frequency conversion (no photon gain)according to embodiments of the present invention. This nondegeneratethree-wave mixing device could be used as part of the lossless microwaveswitch but it does not conserve the frequency of the transmitted signal.Also, the scattering parameters depend on the pump amplitude in FIG. 3.The nondegenerate three-wave mixer can be a Josephson parametricconverter (JPC).

On resonance, the nondegenerate three-wave mixer (e.g., JPC) satisfiesthe following scattering matrix when operated in noiseless frequencyconversion:

${\lbrack S\rbrack = {\begin{pmatrix}r & t \\t^{\prime} & r\end{pmatrix} = \begin{pmatrix}{\cos\;\theta} & {{ie}^{i\;\varphi_{P}}\sin\;\theta} \\{{ie}^{i\;\varphi_{P}}\sin\;\theta} & {\cos\;\theta}\end{pmatrix}}},$

where tan h(iθ/2)=i|ρ| and ρ is a dimensionless pump amplitude (variesbetween 0 and 1).

As a modification to the nondegenerate three-wave mixer and as furtherrecognized herein, the phase of the pump φ_(p) (which can be denoted asφ₁ and φ₂ for two pump signals) will be utilized in accordanceembodiments of the present invention. Since the scattering matrix isunitary, the following relation holds |r|²+|t|²=1, where r is thereflection coefficient, t is the transmission parameter, and t′=−t*(where t* is the conjugate of t). Unitary means that the nondegeneratethree wave mixer preserves the energy and the coherence of the phase.The full conversion working point of the superconducting nondegeneratethree-wave mixing device is |r|²=0, |t|²=1. At the full conversionworking point, there is no reflection and there is full transmissionwith frequency conversion.

In FIG. 3, the superconducting nondegenerate three-wave mixing devicehas 3 ports, which are the Signal port (S), the Idler port (I), and thepump port (P). The superconducting nondegenerate three-wave mixingdevice has transmission t from Idler port to Signal port andtransmission t′ from Signal port to Idler port. From Idler to Signalport, the Idler microwave signal enters the Idler port at frequency f₂,is down converted, and exits the Signal port at frequency f₁. FromSignal to Idler port, the Signal microwave signal enters the Signal portat frequency f₁, is up converted, and exits the Idler port at frequencyf₂. The pump microwave signal provides the energy for frequency upconversion and frequency down conversion. The pump frequency is f_(p),where f_(p)=f₁−f_(s)=f₂−f₁.

FIG. 4 depicts a (superconducting) lossless variable-transmissiontwo-port microwave switch 400 according to embodiments of the presentinvention. The microwave switch 400 includes two nondegenerate Josephsonthree-wave mixers 402_1 and 402_2. The microwave switches 402_1 and402_2 are designed to be the same. For example, the microwave switches402_1 and 402_2 are identical or nominally identical. The microwaveswitches 402_1 and 402_2 each have functionally equivalent ports a, b,and p, which are labeled as ports a1, b1, and p1 for microwave switch402_1 and ports a2, b2, and p2 for microwave switch 402_2. A 90° hybridcoupler 404 is connected to ports a1 and a2 of microwave switches 402_1and 402_2, respectively. The ports a1 and a2 each are connected to theirrespective resonators, such as Signal (S) resonators of Josephsonparametric converters. The ports b1 and b2 are each connected to theirrespective resonators, such as Idler (I) resonators of Josephsonparametric converters. In the three-wave mixers 402_1, the Signal andIdler resonators are connected to a Josephson ring modulator. Similarly,in the three-wave mixers 402_2, the Signal and Idler resonators areconnected to a Josephson ring modulator. The pump ports p1 and p2 can beconnected to on-chip flux lines in the form of short-circuited coupledstriplines that are capacitively coupled to two adjacent nodes of theJRM 1510. Such pump lines can both support microwave tones at the pumpfrequency and dc currents that flux bias the JRMs 1510 in the three-wavemixers 402_1 and 402_2. In one implementation, the pump ports p1 and p2can be connected to the other end of Signal resonator (i.e., notconnected to the end with ports a1 and a2). In one implementation, thepump ports p1 and p2 can be connected to the other end of the Idlerresonator (i.e., not connected to the end with ports b1 and b2).

The two nondegenerate three-wave mixing Josephson elements 402_1 and402_2 are coupled back-to-back by ports b1 and b2 with or without adelay line (depicted as delay line 902 in FIG. 9) in between. Port 1 andport 2 are ports of the 90° hybrid coupler 404. Port 1 is the input portwhen port 2 is the output port assuming the signal flow is from port 1to port 2. Conversely, when the signal flow is in the oppositedirection, port 1 is the output port while port 2 is the input port. Thetwo nondegenerate three-wave mixing Josephson elements 402_1 and 402_2perform upconversion/downconversion of signals in transmission. Thenondegenerate three-wave mixing devices 402_1 and 402_2 are operated innoiseless frequency conversion mode (i.e., no photon gain), and bothdevices 402_1 and 402_2 are operated at the same working point, i.e.,have equal reflection parameters and equal amplitude for theirtransmission parameter. Thus, the nondegenerate three-wave mixingdevices function as active beam splitters. The active beam splitter hasthree physically separated ports. For example, ports a1 and a2 supportsignals at f₁. Ports b1 and b2 support signals at f₂. The pump ports p1and p2 allow for feeding the pump drive. The pump frequency f_(p) isequal to the frequency difference between f₂ and f₁ such thatf_(p)=f₂−f₁. For example, pump port p1 of device 402_1 receives a pumpsignal/drive (pump signal 1) at pump frequency f_(p) and phase φ₁. Pumpport p2 of device 402_2 receives a pump signal/drive (pump signal 2) atpump frequency f_(p) and phase φ₂. The microwave switch 400 is designedto operate as an open switch (i.e., reflection of signal), closed switch(transmission of signal), and/or variable transmission-reflection(transmission of a portion of the signal while reflecting the remainingportion of the signal) based on the pump phase difference between thepump signals feeding pump port p1 of three-wave mixer 402_1 and pumpport p2 of three-wave mixer 402_2. The pump phase difference is definedas ≡φ₁−φ₂. The phase difference between the pump drives feeding the twonondegenerate three-wave mixing Josephson devices 402_1 and 402_2 (viapump port p1 and p2, respectively) induces a nonreciprocal phase shiftto signals (e.g., signal at f₁ through ports 1 and 2) traversing thedevice 400.

FIG. 4 illustrates the superconducting microwave switch 400 intransmission mode, which means that a signal at frequency f₁ is inputinto port 1 of the hybrid coupler 404, is transmitted via the coupler404 to three-wave mixers 402_1 and 402_2, and is output through port 1.Conversely, the signal at frequency f₁ can be input into port 2 of thehybrid coupler 404, be transmitted via the coupler 404 to the three-wavemixers 402_1 and 402_2, and be output through port 2. In this example,the superconducting microwave switch 400 acts as a closed switch formicrowave signals.

FIG. 5 depicts a lossless variable-transmission two-port microwaveswitch 400 according to embodiments of the present invention. FIG. 5depicts an example in which the microwave switch 400 is in reflectionmode, i.e., operating as an open switch. The phase difference betweenthe pump drives feeding the two nondegenerate three-wave mixingJosephson devices 402_1 and 402_2 (via pump port p1 and p2,respectively) determines if the switch is in the open or closed state.In this example, it is assumed that a signal at frequency f₁ is inputinto port 1 of the hybrid coupler 404. The signal at f₁ is reflectedback at port 1 and does not output through port 2. Conversely, when thesignal at f₁ is input to port 2, the signal reflects back to port 2 andis not allowed to be output through port 1.

FIG. 6 depicts a lossless variable-transmission two-port microwaveswitch 400 with a modification to how the pump signal is fed accordingto embodiments of the present invention. The microwave switch 400 inFIG. 6 includes the elements FIG. 5. Additionally, the microwave switch400 includes a 180° hybrid coupler 602 for the pump signal at pumpfrequency f_(p). Also, the microwave switch 400 can include a variablephase shifter 604 on one arm of the pump feeding the two three-wavemixers 402_1 and 402_2. After passing through the 180° hybrid coupler602, the phase shifter 604 causes a phase difference φ between the pumpsignal feeding port p1 and port p2. Therefore, the pump phase differenceφ between the pump drives feeding the two nondegenerate three-wavemixing Josephson devices 402_1 and 402_2 (via pump port p1 and p2,respectively) induces the nonreciprocal phase shift to signals (e.g.,signal at f₁ through ports 1 and 2) traversing the device 400.

As an example of operating the microwave switch 400 with the 180° hybridcoupler 602, the pump signal at pump frequency f_(p) is received at theΣ port of the 180° hybrid coupler 602 and is split. One-half of the pumpsignal travels down the straight bar of the 180° hybrid coupler 602 topump port p1 with a 0° phase shift and the other half travels down thecross bar to pump port p2 with a 0° phase shift. Before reaching portp2, the pump signal undergoes a phase shift (at frequency f_(p)) causedby the variable phase shifter 604. The phase shift by the variable phaseshifter 604 causes the phase φ₂ of pump signal entering port p2 of thethree-wave mixer 402_2 to be different from the phase φ₁ of the pumpsignal entering port p1 of the three-wave mixer 402_1. Moreover, withoutrequiring two separate pump signals/drives to be input as in FIGS. 4 and5, the 180° hybrid coupler 602 is configured to use one pump signal tocreate the two separate pump signals (pump 1 and pump 2) at frequencyf_(p) such that the variable phase shifter 604 creates the phasedifference φ=φ₁−φ₂ between pump signal 1 entering port p1 and pumpsignal 2 entering port p2. As discussed herein, the phase differencedetermines whether the signal at frequency f₁ entering port 1 will beoutput through port 2 or whether the signal will be reflected back toport 1. Conversely, the phase difference determines whether the signalat frequency f₁ entering port 2 will be output through port 1 or whetherthe signal will be reflected back to port 2. The phase shifter 604 canbe implemented in various ways. Examples of the phase shifter 604include two coupled Josephson parametric converters operated in fullfrequency conversion and a half-wavelength superconducting resonatorwith a dc-SQUID (direct current superconducting quantum interferencedevice) embedded at its center. In the former example, the phasedifference between the pumps feeding the two JPCs determines the phaseshift of the transmitted signals, whereas in the latter example, bytuning the flux threading the dc-SQUID the resonance frequency of theresonator is shifted, which, in turn, shifts the phase of thetransmitted signal through the resonator. It is noted that FIG. 15illustrates an implementation of FIGS. 4, 5, and 6 without showing thehybrid couplers 404 and 602, for simplicity and conciseness.

FIG. 7 depicts a lossless variable-transmission two-port microwaveswitch 400 according to embodiments of the present invention. In thethree-wave mixer 402_1, port a1 connects to one end of the resonator(e.g., Signal resonator) and the other end is connected to ground.Particularly, the resonator (e.g., Signal resonator) has two feedlines,where one feedline connects to the 90° hybrid coupler 404 (as in FIGS. 4and 5) and one feedline is connected (shorted) to ground (the sameanalogously applies to mixer 402_2). In FIGS. 4 and 5, the Signalresonator is connected to one feedline which is one leg of the 90°hybrid coupler 404 (unlike FIG. 7), so only a single port a1 is shownfeeding the resonator in the mixer 402_1 (the same analogously appliesfor mixer 402_2).

Similarly, for port b1 (the same applies analogously to port b2 in mixer402_2), port b1 connects to one end of the resonator (e.g., Idlerresonator) and the other end is connected to ground. Particularly, theresonator (e.g., Idler resonator) has two feedlines, where one feedlineconnects to one feedline of the other idler resonator (as in FIGS. 4 and5) and one feedline is connected (shorted) to ground. By connecting onefeedline to ground, the idler or signal resonator is single ended,meaning the input and output signals of the resonator are carried by onefeedline only. Just as discussed above, the pump signal 1 is applied atfrequency f_(p) and phase φ₁ to port p1 while the pump signal 2 isapplied at frequency f_(p) and phase φ₂ to port p2, in order to createthe phase difference φ. The phase difference determines the operation ofthe microwave switch 400. Just as discussed in FIG. 4, thesuperconducting microwave switch 400 in FIG. 7 can operate intransmission mode, which means that the signal at frequency f₁ is inputinto port 1 of the hybrid coupler 404, is transmitted via the coupler404 to three-wave mixers 402_1 and 402_2, and is output through port 2.Conversely, the signal at frequency f₁ can be input into port 2 of thehybrid coupler 404, be transmitted via the coupler 404 to the three-wavemixers 402_1 and 402_2, and be output through port 1. Additionally, justas discussed in FIG. 5, the superconducting microwave switch 400 in FIG.7 can operate in reflection mode. For the signal at frequency f₁ inputinto port 1 of the hybrid coupler 404, the signal at f₁ is reflectedback at port 1 and does not output through port 2. Conversely, when thesignal at f₁ is input to port 2, the signal reflects back to port 2 andis not allowed to be output through port 1. It is noted that FIG. 16illustrates one implementation of FIG. 7 without showing the hybridcouplers 404 and 602, for simplicity and conciseness.

FIG. 8 depicts a lossless variable-transmission two-port microwaveswitch 400 with a modification to how the pump signal is fed accordingto embodiments of the present invention. The microwave switch 400 inFIG. 8 includes the elements discussed herein. In the two three-wavemixers 402_1 and 402_2, ports a1 and a2 connect to two ends of theirrespective resonator (e.g., Signal resonators) and the resonator has twofeedlines, where one feedline connects to the 90° hybrid coupler 404 andone feedline is connected (shorted) to ground. Similarly, for ports b1and b2 in mixers 402_1 and 402_2, ports b1 and b2 connect to two ends oftheir respective resonators (e.g., Idler resonators) and the resonatorhas two feedlines, where one feedline connects to one feedline of theother idler resonator and one feedline is connected (shorted) to ground.

The modified three-wave mixers 402_1 and 402_2 are connected to the 180°hybrid coupler 602 for receiving the pump signal at pump frequency f_(p)(as discussed in FIG. 6), and the microwave switch 400 includes thevariable phase shifter 604 on one arm of the pump feeding the twothree-wave mixers 402_1 and 402_2. The function of the 180° hybridcoupler 602 operates as discussed herein.

One option for implementing a variable phase shifter on-chip is using asymmetric two-port resonator with a dc-SQUID at its center, whosemaximum frequency is equal to the pump frequency. By slightly shiftingthe resonance frequency within the resonator bandwidth, the phase of thetransmitted pump can be shifted between 0° to 90°. One challenge ofusing this option is balancing the amplitude of the pump feeding theother JPC stage because the amplitude of the transmitted pump Signalthrough the resonator is expected to be attenuated in the range 0-3 dBwhen the resonance frequency is shifted.

FIG. 9 depicts a signal flow graph of the superconducting microwaveswitch/device 400 according to embodiments of the present invention. Thetwo ports b1 and b2 of the mixers 402_1 and 402_2 (two active beamsplitters) which support signals at f₂ are connected together through adelay line 902 (e.g., a lossless transmission line). In oneimplementation, the delay line 902 is not present. The signal flow graphshows the signal flow through ports 1 and 2, the 90° hybrid coupler 404,the mixer 402_1, the mixer 402_2, and the delay line 902. The scheme forthe signal flow is lossless. The lossless delay line 902 should have aneffective electrical length of multiples of π radians at the frequencyof the ports b1 and b2 that are connected together. The two active beamsplitters are (assumed to be) nominally identical. The scatteringparameters of the microwave device 400 at a certain working point aredetermined by wave interference between 4 principal paths (althoughthere are multiple (or infinite paths)). The scattering parameter onresonance from port i to j (where i,∈{1, 2}) vanishes if the waves thatpropagate from i to j interfere destructively. The scattering parameteron resonance from port i to j (where i,∈{1, 2}) is almost unity if thewaves that propagate from i to j interfere constructively.

The pump is assumed to be enabled where |r|²+|t|²=1 and the phasedifference is ≡φ₁−φ₂. The phase shift is defined as α=e^(iφ) ^(d) .Phase shift acquired by signals propagating along the transmission line902 (between ports b1 and b2) at f₂ is φ_(d)=ω₂τ_(d). The angularfrequency of microwave signals at f₂ is ω₂=2πf2. The delay time of thedelay/transmission line 902 is τ_(d)=ld√{square root over (ε)}/c, wherec is the speed of light, l_(d) is the effective electrical length of thetransmission line (902), and ε is the effective dielectric constant ofthe transmission line.

In the signal graph of FIG. 9, r₁ and r₂ are the reflectioncoefficients, t₁, t′₁, t₂, and t′₂ are the transmission parameters ofmixers 402_1 and 402_2 respectively, where t′₁=−t*₁ (where t*₁ is theconjugate of t₁) and where t′₂=−t*₂ (where t*₂ is the conjugate of t₂).It is presumed that t₁ is equal to or about equal t₂ and r₁ is equal toor about equal to r₂.

It should be appreciated that there are numerous paths for the signal atf₁ entering the port 1 to follow in the microwave switch 400 and/or thesignal at f₁ entering the port 2 to follow. For any signal at f₁entering the port 1 or port 2, wave interference results in 4 principalpaths that determine transmission and/or reflection, based on the phasedifference φ.

For ease of understanding and explanation, headings are utilized below.It should be appreciated that the headings are not meant to be limiting.

I. Device Equations Based on the Signal Flow Graph

The following are device equations for the microwave switch 400 based onthe signal flow graph according to embodiments of the present invention.

First, using the scattering matrix

${\lbrack S\rbrack = \begin{pmatrix}S_{11} & S_{12} \\S_{21} & S_{22}\end{pmatrix}},$the scattering parameters on the diagonal are S₁₁ and S₂₂ which definethe reflection parameters. The scattering parameters on the off diagonalare S₂₁ and S₂₂ which define the transmission parameters. The results ofthe S matrix are (Equations A)

$S_{11} = {\frac{1}{2}\left( {S_{a\; 1\; a\; 1} - S_{a\; 2\; a\; 2} + {iS}_{a\; 2\; a\; 1} + {iS}_{a\; 1\; a\; 2}} \right)}$$S_{22} = {\frac{1}{2}\left( {S_{a\; 2\; a\; 2} - S_{a\; 1\; a\; 1} + {iS}_{a\; 2\; a\; 1} + {iS}_{a\; 1\; a\; 2}} \right)}$$S_{21} = {\frac{1}{2}\left( {{iS}_{a\; 1\; a\; 1} + {iS}_{a\; 2\; a\; 2} + S_{a\; 2\; a\; 1} - S_{a\; 1\; a\; 2}} \right)}$$S_{12} = {\frac{1}{2}\left( {{iS}_{a\; 1\; a\; 1} + {iS}_{a\; 2\; a\; 2} + S_{a\; 1\; a\; 2} - S_{a\; 2\; a\; 1}} \right)}$

Intermediate results are

$S_{a\; 1\; a\; 1} = {r_{1} + \frac{r_{2}t_{1}t_{1}^{\prime}\alpha^{2}}{1 - {r_{1}r_{2}\alpha^{2}}}}$$S_{a\; 1\; a\; 2} = \frac{t_{1}t_{2}^{\prime}\alpha}{1 - {r_{1}r_{2}\alpha^{2}}}$$S_{a\; 2\; a\; 2} = {r_{2} + \frac{r_{1}t_{2}t_{2}^{\prime}\alpha^{2}}{1 - {r_{1}r_{2}\alpha^{2}}}}$$S_{a\; 2\; a\; 1} = \frac{t_{2}t_{1}^{\prime}\alpha}{1 - {r_{1}r_{2}\alpha^{2}}}$

which can be rewritten as (Equations B)

$S_{a\; 1\; a\; 1} = {r_{1} - \frac{e^{2\; i\;\varphi_{d}}r_{2}{t_{1}}^{2}}{1 - {r_{1}r_{2}e^{2\; i\;\varphi_{d}}}}}$$S_{a\; 1\; a\; 2} = {- \frac{{t_{1}}{t_{2}^{\prime}}e^{i{({\varphi_{d} - \varphi})}}}{1 - {r_{1}r_{2}e^{2\; i\;\varphi_{d}}}}}$$S_{a\; 2\; a\; 2} = {r_{2} - \frac{e^{2\; i\;\varphi_{d}}r_{1}{t_{2}}^{2}}{1 - {r_{1}r_{2}e^{2\; i\;\varphi_{d}}}}}$$S_{a\; 2\; a\; 1} = {- \frac{{t_{2}}{t_{1}^{\prime}}{\alpha }e^{i{({\varphi_{d} + \varphi})}}}{1 - {r_{1}r_{2}e^{2\; i\;\varphi_{d}}}}}$

where ≡φ₁−φ₂.

It should be noted that, for example, the nomenclature S₂₁ represents ascattering parameter (transmission parameter) for a signal (at frequencyf₁) entering from port 1 and exiting port 2, as understood by oneskilled in the art. Similarly, for example, the nomenclature S_(a1a2)represents a scattering parameter (transmission parameter) for a signalentering port a2 and exiting port a1. As can be seen in the equationsabove, S₁₁, S₂₂, S₂₁, and S₁₂ each have 4 principal paths given the waveinterference as understood by one skilled in the art, although theactual different possible paths between port 1 and 2 (and vice versa) isnumerous or infinite because of the self loop between the idlerresonators (e.g., between coupled ports b1 and b2). However, thescattering parameters in Equations B account for all possible paths andsubsequently the scattering parameters for the whole device in EquationsA. Additionally, the scattering parameters S₁₁ and S₂₁ define theoperation of the microwave switch 400 for a signal (at frequency f₁)entering port 1 which then exits port 1 or exits port 2 respectively.Likewise, scattering parameters S₂₂ and S₁₂ define the operation of themicrowave switch 400 for a signal (at frequency f₁) entering port 2which then exits port 2 or exits port 1 respectively.

II. Special Case of Nominally Identical Mixers Operated at the SameWorking Point

Now, turning to a special case of nominally identical mixers 402_1 and402_2 operated at the same working point, the following relations aresatisfied r₁=r₂=r, |t₁|=|t₁′|=|t₂|=|t₂′|=t (which means that the mixers402_1 and 402_2 are balanced), φ≡φ₁−φ₂, and |r|²+|t|²=1. In this specialcase, the results of the S matrix are

$S_{a\; 1\; a\; 1} = {S_{a\; 2\; a\; 2} = {r\frac{1 - e^{2\; i\;\varphi_{d}}}{1 - {r^{2}e^{2\; i\;\varphi_{d}}}}}}$$S_{a\; 1\; a\; 2} = {- \frac{t^{2}e^{i{({\varphi_{d} - \varphi})}}}{1 - {r^{2}e^{2i\;\varphi_{d}}}}}$$S_{a\; 2\; a\; 1} = {- \frac{t^{2}e^{i{({\varphi_{d} + \varphi})}}}{1 - {r^{2}e^{2i\;\varphi_{d}}}}}$

which results (finally) in

$S_{11} = {S_{22} = {{- \frac{{it}^{2}e^{i\;\varphi_{d}}}{1 - {r^{2}e^{2\; i\;\varphi_{d}}}}}{\cos(\varphi)}}}$$S_{21} = {\frac{i}{1 - {r^{2}e^{2\; i\;\varphi_{d}}}}\left( {{r\left( {1 - e^{2\; i\;\varphi_{d}}} \right)} - {t^{2}e^{i\;\varphi_{d}}{\sin(\varphi)}}} \right)}$$S_{12} = {\frac{i}{1 - {r^{2}e^{2\; i\;\varphi_{d}}}}\left( {{r\left( {1 - e^{2\; i\;\varphi_{d}}} \right)} + {t^{2}e^{i\;\varphi_{d}}{\sin(\varphi)}}} \right)}$

III. Special Case of Nominally Identical Mixers Operated at the SameWorking Point

Again, for a special case of nominally identical mixers 402_1 and 402_2operated at the same working point, the following relations aresatisfied r₁=r₂=r, |t₁|=|t₁′|=|t₂|=|t₂′|=t (which means that the mixers402_1 and 402_2 are balanced), φ≡φ₁−φ₂, and |r|²+|t|²=1.

Additionally, for phase shifts acquired by on-resonance signals (for theidler resonators) at f₂ propagating along the transmission lineφ_(d)=πk, where k=0, ±1, ±2, . . . , the scattering parameters are asfollows (Equations C):

S_(a 1a 1) = S_(a 2 a 2) = 0${{Sa}\; 1a\; 2} = {{- \frac{t\; 2\; e^{i\;\varphi_{d}}e^{{- i}\;\varphi}}{1 - {r\; 2}}} = {- e^{{- i}\;\varphi}}}$$S_{a\; 2\; a\; 1} = {{- \frac{t^{2}e^{i\;\varphi_{d}}e^{i\;\varphi}}{1 - r^{2}}} = {- e^{i_{\varphi}}}}$

which then results inS ₁₁ =S ₂₂ =−ie ^(iφ) ^(d) cos(φ)S ₂₁ =−ie ^(iφ) ^(d) sin(φ)S ₁₂ =ie ^(iφ) ^(d) sin(φ)

Regardless of the values of r and t, as long a t>0 and r<1, themicrowave switch 400 is turned on. The S matrix is

$\lbrack S\rbrack = {- {i\begin{pmatrix}{\cos(\varphi)} & {- {\sin(\varphi)}} \\{\sin(\varphi)} & {\cos(\varphi)}\end{pmatrix}}}$

where −i is a global phase, which can be ignored. In an implementation,the global phase can be chosen arbitrarily and/or cannot be measured.

For the case when φ_(d)=0, the scattering parameters simplifies to(Equations D):S ₁₁ =S ₂₂=cos(φ)S ₂₁=−sin(φ)S ₁₂=sin(φ)

As can be seen, these equations show that the scattering parameters ofthe S matrix are dependent upon the phase difference φ of the pumpsignals, thereby determining whether there is a 1/−1 on the diagonal(meaning reflection, i.e., open switch), which is achieved for φ=πk,where k=0, ±1, ±2, . . . , or whether there is a 1/−1 on the offdiagonal (meaning transmission, i.e., a closed switch), which isachieved for φ=(2k+1)*π/2, where k=0, ±1, ±2, . . . . This result alsoshows that for φ that is between 0 and π/2 (or π/2 and π, and so forth)the switch can have variable reflection-transmission parameters. Forexample, for φ=π/4, the amplitude of the reflection and transmissionparameters is equal to 1/√{square root over (2)}, which means the switchat this working point would function as a 50:50 beam-splitter: half ofthe signal power would be reflected back to the port of origin and halfwould be transmitted to the other port.

FIG. 10A depicts an example of the microwave switch 400 at a workingpoint according to embodiments of the present invention. FIG. 10Bdepicts an example of the microwave switch 400 at the same working pointas in FIG. 10A except for having a different phase difference accordingto embodiments of the present invention. The microwave switch 400 is amultipath interferometric Josephson Switch (MPIJSW). FIG. 10Aillustrates the microwave switch 400 as an open switch. In FIG. 10A, thenondegenerate microwave mixers that are part of the microwave switch 400are operating at a 50:50 beam splitter point. In FIGS. 10A and 10B(discussed below), the three-wave mixers 402_1 and 402_2 are nominallyidentical (i.e., balanced or the same) and the amplitudes of theirscattering parameters are given by r₁=r₂=r=1/√{square root over (2)} and|t₁|=|t₁′|=|t₂|=|t₂′|=|t|=1/√{square root over (2)}. In the microwaveswitch 400 (of FIGS. 10A and 10B), the transmission amplitude of thedelay line 902 is |α|=1, while the phase shift acquired by propagatingalong the transmission line 902 at f₂ is φ_(d)=0 (on resonance). InFIGS. 10A and 10B, the scattering matrix is

$\lbrack S\rbrack = {- {{i\begin{pmatrix}{\cos(\varphi)} & {- {\sin(\varphi)}} \\{\sin(\varphi)} & {\cos(\varphi)}\end{pmatrix}}.}}$In FIG. 10A, the phase difference in the pump signal(s) is φ=0 (which isdifferent than in FIG. 10B). For φ=0, the scattering matrix becomes

${\lbrack S\rbrack = \begin{pmatrix}1 & 0 \\0 & 1\end{pmatrix}},$which shows ones (1's) on the diagonal (r) as an indication ofreflection, thus being an open switch.

FIG. 10B depicts an example of the microwave switch 400 at the workingpoint according to embodiments of the present invention. FIG. 10Bincludes the same parameters for the switch 400 as in FIG. 10A but FIG.10B is a closed switch. However, in FIG. 10B, the phase differencebetween the pump signals is φ=π/2, resulting in the scattering matrix

${\lbrack S\rbrack = \begin{pmatrix}0 & {- 1} \\1 & 0\end{pmatrix}},$which shows ones (1's) on the off diagonal (t) as an indication oftransmission.

FIG. 11A depicts an example of the microwave switch 400 at a workingpoint according to embodiments of the present invention. FIG. 11Bdepicts an example of the microwave switch 400 at the same working pointas in FIG. 11A except for having a different phase difference φaccording to embodiments of the present invention.

FIG. 11A illustrates the microwave switch 400 as an open switch. In FIG.11A, the nondegenerate microwave mixers that are part of the microwaveswitch 400 are operating at a 25:75 beam splitter point, which meansthat each mixer reflects ¼ of the signal power back to the origin portand transmits ¾ of the signal power to the other port with frequencyconversion. In FIGS. 11A and 11B (discussed below), the three-wavemixers 402_1 and 402_2 are nominally identical (i.e., balanced or thesame) and the amplitudes of their scattering parameters are given byr₁=r₂=r=½ and |t₁|=|t₁′|=|t₂|=|t₂′|=|t|=3/4. In the microwave switch 400(of FIGS. 10A and 10B), the transmission amplitude of the delay line 902is |α|=1, while the phase shift acquired by propagating along thetransmission line 902 at f₂ is φ_(d)=0 (on resonance). In FIGS. 11A and11B, the scattering matrix is

$\lbrack S\rbrack = {- {{i\begin{pmatrix}{\cos(\varphi)} & {- {\sin(\varphi)}} \\{\sin(\varphi)} & {\cos(\varphi)}\end{pmatrix}}.}}$In FIG. 11A, the phase difference in the pump signal(s) is φ=0 (which isdifferent than in FIG. 11B). For φ=0, the scattering matrix becomes

${\lbrack S\rbrack = \begin{pmatrix}1 & 0 \\0 & 1\end{pmatrix}},$which shows ones (1's) on the diagonal (r) as an indication ofreflection, thus being an open switch.

FIG. 11B depicts an example of the microwave switch 400 at the workingpoint according to embodiments of the present invention. FIG. 11Bincludes the same parameters for the switch 400 as in FIG. 11A but FIG.11B is a closed switch because of the phase difference. Particularly, inFIG. 11B, the phase difference between the pump signals is φ=π/2,resulting in the scattering matrix

${\lbrack S\rbrack = \begin{pmatrix}0 & {- 1} \\1 & 0\end{pmatrix}},$which shows ones (1's) on the off diagonal (t) as an indication oftransmission.

It should be recognized that the microwave device 400 can be controlledto be an open switch or a closed switch according to the phasedifference as seen in FIGS. 10A, 10B, 11A, and 11B.

Now, turning to illustrations of wave interference, the microwave switch400 is a multi-path interferometric Josephson switch (MPIJSW). Forexplanation purposes, a few multi-path interference examples (withrespect to the phase) are provided for the microwave switch 400. FIGS.12A, 12B, 12C, and 12D illustrate principal paths 1, 2, 3, and 4respectively for S₂₁ according to embodiments. As noted above, thepropagation of the signal for S₂₁ denotes that the signal at frequencyf₁ is intended to propagate from port 1 to port 2 of the microwaveswitch 400. FIGS. 12A, 12B, 12C, 12D depict the 4 principal paths fromport 1 to port 2 for the two three-wave mixers 402_1 and 402_2, whichresult in constructive interference. The three-wave mixers 402_1 and402_2 are nominally identical (or balanced) unless noted otherwise. Inthis case r<1 and t>0, which means that the three-wave mixers 402_1 and402_2 (JPCs) are ON. Also, the phase shift acquired by signalspropagating along the transmission line 902 (in any direction betweenports b1 and b2) at f₂ is φ_(d)=0 and the phase difference between pump1 and pump 2 is φ=π/2.

FIG. 12A depicts path 1 of the microwave switch 400 for S₂₁ according toembodiments of the present invention. A signal at frequency f₁ andrelative phase 0 is input to port 1 of the microwave switch 400 and thisinput is denoted as 1∠0°, which means that its normalized amplitude is 1and its relative phase is 0°. Path 1 is illustrated. The destructivewave interference in this path results in a zero amplitude at port 2, asseen in Equations C.

FIG. 12B depicts path 2 of the microwave switch 400 for S₂₁ according toembodiments of the present invention. For the signal at frequency f₁ andrelative phase 0 (1∠0°) input to port 1 of the microwave switch 400, thepath 2 is illustrated and the destructive wave interference along thispath results in a zero-amplitude transmitted signal along this path (atport 2), as seen in Equations C.

FIG. 12C depicts path 3 of the microwave switch 400 for S₂₁ according toembodiments of the present invention. For the signal at frequency f₁ andrelative phase 0 (1∠0°) input to port 1 of the microwave switch 400, thepath 3 is illustrated and the transmitted signal along this path at port2 due to wave interference is

$\frac{1}{2}{{\angle 0{^\circ}}.}$This means its normalized amplitude is ½ and its relative phase is 0°.

FIG. 12D depicts path 4 of the microwave switch 400 for S₂₁ according toembodiments of the present invention. For the signal at frequency f₁ andrelative phase 0 (1∠0°) input to port 1 of the microwave switch 400, thepath 4 is illustrated and the transmitted signal along this path at port2 due to wave interference is

$\frac{1}{2}{{\angle 0{^\circ}}.}$This means its normalized amplitude is ½ and its relative phase is 0°.

The constructive interference between the 4 principal paths in FIGS.12A-12D is

${S_{21}} = {{{2 \cdot \frac{1}{2}}} = 1.}$For the case when φ_(d)=0 and φ=π/2, the multi-path interference of S₂₁can also be obtained by using the result shown in Equations D havingS₂₁=−i sin(φ), which results in an amplitude of |−1i|=1.

Now, turning to other illustrations of wave interference for themicrowave switch 400, FIGS. 13A, 13B, 13C, and 13D illustrate principalpaths 1, 2, 3, and 4 respectively for S₂₂ according to embodiments. Thepropagation of the signal for S₂₂ denotes that the signal at frequencyf₁ is intended to propagate from port 2 to port 2 of the microwaveswitch 400. FIGS. 13A, 13B, 13C, 13D depict the 4 principal paths fromport 2 to port 2 for the two three-wave mixers 402_1 and 402_2, whichresult in destructive interference. The three-wave mixers 402_1 and402_2 are nominally identical (or balanced) unless noted otherwise. Inthis case r<1 and t>0, which means that the three-wave mixers 402_1 and402_2 (JPCs) are ON. Also, the phase shift acquired by signalspropagating along the transmission line 902 (in any direction betweenports b1 and b2) at f₂ is φ=0 and the phase difference between pump 1and pump 2 is φ=π/2.

FIG. 13A depicts path 1 of the microwave switch 400 for S₂₂ according toembodiments of the present invention. A signal at frequency f₁ andrelative phase 0 is input to port 2 of the microwave switch 400 and thisinput is denoted as 1∠0°, which means its normalized amplitude is 1 andits relative phase is 0. Path 1 is illustrated. The destructive waveinterference in this path results in a zero amplitude at port 2, as seenin the Equations C.

FIG. 13B depicts path 2 of the microwave switch 400 for S₂₂ according toembodiments of the present invention. For the input signal at frequencyf₁ and relative phase 0 (1∠0°) input to port 2 of the microwave switch400, the path 2 is illustrated and the destructive wave interferencealong this path results in a zero amplitude return signal at port 2 asseen in the Equations C.

FIG. 13C depicts path 3 of the microwave switch 400 for S₂₂ according toembodiments of the present invention. For the input signal at frequencyf₁ and relative phase 0 (1∠0°) input to port 2 of the microwave switch400, the path 3 is illustrated and the constructive wave interferenceresults in a return signal along this path with amplitude and phase

$\frac{1}{2}{\angle 180{^\circ}}$at port 2. This means its normalized amplitude is ½ and its relativephase is 180°. This result can be seen in Equations C above as well asfrom the fact that the signal passes through the hybrid twice whichattenuates it power by a factor 2.

FIG. 13D depicts path 4 of the microwave switch 400 for S₂₂ according toembodiments of the present invention. For the input signal at frequencyf₁ and relative phase 0 (1∠0°) input to port 2 of the microwave switch400, the path 4 is illustrated and the constructive wave interferenceresults in a return signal along this path with amplitude and phase

$\frac{1}{2}{\angle 0{^\circ}}$at port 2. This means its normalized amplitude is ½ and its relativephase is 180°. This result can be seen in the Equations C above as wellas from the fact that the signal passes through the hybrid twice whichattenuates it power by a factor 2.

The destructive interference between the 4 principal paths in FIGS.13A-13D is

${S_{22}} = {{{\frac{1}{2} - \frac{1}{2}}} = 0.}$For the case when φ_(d)=0 and φ=π/2, the multi-path interference of S₂₁can also be obtained by using S₂₂=−i cos(φ), which results in 0.

It is noted that the amplitude of the pump signal (whether pump signal 1and pump signal 2 or a 180 hybrid coupler is utilized to split a singlepump signal into pump signals 1 and 2) is utilized to operate thethree-wave mixers employed in the device 400 and set their transmissiont and reflection r parameters, but what determines whether the switch400 is open, closed, or operating in a variable transmission-reflectionamplitude switch mode in the embodiments of the present invention is thephase difference between the pump drives. It is again noted that athree-wave mixer scattering matrix

${\lbrack S\rbrack = {\begin{pmatrix}r & t \\t^{\prime} & r\end{pmatrix} = \begin{pmatrix}{\cos\;\theta} & {{ie}^{{- i}\;\varphi_{P}}\sin\;\theta} \\{{ie}^{i\;\varphi_{P}}\sin\;\theta} & {\cos\;\theta}\end{pmatrix}}},$where tan h(iθ/2)=i|ρ| and ρ is a dimensionless pump amplitude (variesbetween 0 and 1). The pump amplitude p is given as a function of theangle θ, which determines the reflection and transmission parameters.

The microwave switch 400 supports five operation modes, under thefollowing conditions which are 1) r₁=r₂=r, 2) |t₁|=|t₁′|=|t₂|=|t₂|=t, 3)φ≡φ₁−φ₂, 4) |r|²+|t|²=1, 5) φ_(d)=πk, where k=0, ±1, ±2, . . . , and 6)the hybrid and the coupling transmission lines are lossless. FIG. 14depicts the five operational modes in Table 1400 according toembodiments of the present invention. The modes are given for onresonance signals but also applies for a certain bandwidth aroundresonance which is equal to the bandwidth of the whole device (switch400). The five modes of operation are 1) switch is closed withreciprocal transmission between its ports, 2) switch is closed withnonreciprocal phase shift for the transmitted signal between its ports,3) switch is closed with variable transmission-reflection amplitudebetween its ports, 4) switch is open with unity reflection. For the lastmode, the phase of the reflected signal is equal to the phase of theincident signal, and 5) switch is open with unity reflection. The phaseof the reflected signal is shifted by 180 degree relative to the phaseof the incident signal. The conditions for each mode of operation arelisted in the Table 1400.

FIG. 15 depicts an example of the microwave switch 400 withoutillustrating the 90° hybrid coupler (for simplicity and conciseness)according to embodiments of the present invention. FIG. 16 depicts anexample of the microwave switch 400 without illustrating the 90° hybridcoupler according to embodiments of the present invention. However, itshould be appreciated that the hybrid coupler 404 is connected althoughnot shown. Each of three-wave mixers 402_1 and 402_2 includes aJosephson ring modulator (JRM) 1510 which is a nonlinear dispersiveelement based on (4) Josephson tunnel junctions 1506 in an outer ring(and optionally (4) Josephson tunnel junction 1505) which can performthree-wave mixing of microwave signals at the quantum limit.Particularly, the JRM 1510 consists of four nominally identicalJosephson junctions arranged in a Wheatstone bridge configuration.

In each of the three-wave mixers 402_1 and 402_2, one of the microwaveresonators is depicted as resonator_a 1502 and the other is resonator_b1504. The resonators_a 1502 can be referred to as Signal resonators andthe resonators_b 1504 can be referred to as Idler resonators. Theresonators 1502 and 1504 are shown as transmission lines but theresonators 1502 and 1504 can be lumped elements, etc. In FIGS. 15 and16, the 90° hybrid coupler 404 would be connected to ports a1 and a2.For example, FIG. 17 depicts port a1 from Signal resonator_a 1502 ofmixer 402_1 connected to one leg of the 90° hybrid coupler 404 and porta2 from Signal resonator_a 1502 of mixer 402_2 connected to the oppositeleg of the 90° hybrid coupler 404. FIG. 17 is only a partial view of themicrowave switch 400 illustrating connection of the resonators 1502 tothe hybrid coupler 404.

In FIGS. 15 and 16, the ports b1 and b2 are connected together. In oneimplementation, the delay line 902 could be inserted in between asdiscussed herein. There are various way of feeding the pump signals 1and 2 to the three-wave mixers 402_1 and 402_2 which have equalamplitudes, same frequency f_(p), but have a zero or nonzero phasedifference. As one example, in FIGS. 15 and 16, the pumps p1 and p2 canbe fed to on-chip flux lines (e.g., flux lines 1508) in the form ofshort-circuited coupled striplines that are capacitively coupled to twoadjacent nodes of the JRM 1510. Such pump lines can both supportmicrowave tones at the pump frequency and dc currents that flux bias theJRMs 1510. A low-pass filter 1512 can be coupled in between the pumpport and the flux line 1508 to filter out higher frequency f₁ and f₂.Another way for flux biasing the JRMs is by using external magneticcoils attached to the mixers package and/or using a very small magneticmaterial integrated on chip or in the package. Another way to feed thepump drives is by using an on-chip 3-port power divider thatcapacitively couples to opposite nodes of the JRM 1510. Further, eachresonator_a 1502 and resonator_b 1504 has two ends. FIG. 15 shows thatone end of resonator_a 1502 is open, while the other is capacitivelycoupled to a feedline at point X1 which is port a1 in mixer 402_1.Similarly for mixer 402_2, one end of resonator_a 1502 is open, whilethe other is capacitively coupled to a feedline at point X2 which isport a2 in mixer 402_2. Furthermore, FIG. 15 shows that one end ofresonator_b 1504 is open, while the other is capacitively coupled to afeedline at point Y1 which is port b1 in mixer 402_1. Similarly formixer 402_2, one end of resonator_b 1504 is open, while the other iscapacitively coupled to a feedline at point Y2 which is port a2 in mixer402_2. One open end of the resonator_a 1502 or one open end of theresonator_b 1504 could be utilized to feed the pump signal, by addingweakly coupled feedlines to one of these ends.

Unlike FIG. 15, FIG. 16 shows that one end of resonator_a 1502 iscapacitively coupled to port a1 (port a2 in mixer 402_2), which isconnected to one port of the hybrid, while the other end is capacitivelycoupled to a feedline that is shorted to ground. Similarly, one end ofresonator_1 1504 capacitively couples to port b1 (port b2 in mixer402_2) and the other end is capacitively coupled to a feedline that isshorted to ground. The feedline of the resonator_a 1502 or one feedlineof the resonator_b 1504 that is grounded could possibly be disconnectedfrom ground and instead be utilized to feed the pump signal. In thiscase, the coupling capacitance between the pump feedline and theresonator should be small enough to prevent signal leakage through thisdesignated pump feedline.

In one implementation of FIGS. 15 and 16, the 180° hybrid coupler 602could be connected to pump ports p1 and p2, and the variable phaseshifter 604 can be on one leg.

The circuit elements of the microwave switch 400 and connected to themicrowave switch 400 can be made of superconducting material. Therespective resonators and transmission/feed/pump lines are made ofsuperconducting materials. The hybrid couplers can be made ofsuperconducting materials. Examples of superconducting materials (at lowtemperatures, such as about 10-100 millikelvin (mK), or about 4 K)include niobium, aluminum, tantalum, etc. For example, the Josephsonjunctions are made of superconducting material, and their tunneljunctions can be made of a thin tunnel barrier, such as an oxide. Thecapacitors can be made of superconducting material separated by low-lossdielectric material. The transmission lines (i.e., wires) connecting thevarious elements are made of a superconducting material.

As understood by one skilled in the art, there are many differenttechnical advantages and benefits of the microwave switch 400. Themicrowave switch 400 has more functionalities than any other switch (tobe utilized for superconducting/quantum purposes) which include:reflector with same phase, reflector with phase negation, reciprocaltransmission, nonreciprocal transmission, andvariable-transmission-reflection beam-splitter. The microwave switch 400is lossless, is easy to engineer, design, and fabricate, can be realizedon chip using superconducting circuits or integrated into a PCB. Themicrowave switch 400 can be made broadband by engineering the impedanceof the JPC feedlines, and implementing lumped-element JPCs. Themicrowave switch 400 can be made compact using lumped-element design ofthe hybrids and JPCs and requires no flux control or flux pulses.Additionally, because r and t do not need to be r=0 and t=1, the device400 can be very stable over a long period of time (limited mainly by thedc-flux bias of the two JPCs) and it is easy to tune up. Also, because rand t do not need to be r=0 and t=1, the device 400 can have a largedynamic range (maximum input power) and the pump power feeding thedevice can be relatively small (less heating of the mixing chamber in adilution refrigerator). Furthermore, other than having nominallyidentical JPCs (which is within the standard fabrication capabilities),there are no stringent requirements on uniformity or homogeneity. Themicrowave switch 400 can use one pump for all modes of operation, exceptthe variable transmission-reflection beam splitter mode which requirestwo pump sources or one with phase shifter on one arm. The microwaveswitch 400 can be made using niobium (Nb) junctions and operated at 4K.The microwave switch 400 has fast switching times in the range ofseveral nanoseconds (ns) (which is mainly limited by the bandwidth ofthe JPCs) and has large ON/OFF ratio of more than 20 decibels (dB).

FIG. 18 depicts a flow chart 1800 of a method of forming/configuring amicrowave switch 400 according to embodiments of the present invention.At block 1802, a first nondegenerate device 402_1 includes a first porta1 and a second port b1 and a second nondegenerate device 402_2 includesanother first port a2 and another second port b2, the second port b 1being coupled to the another second port b2. For example, the couplingbetween the second port b 1 and another second port b2 alsorepresents/includes coupling between respective feedlines of, forexample, the idler resonators_b 1504 in devices 402_1 and 402_2. Thefirst nondegenerate device 402_1 and the second nondegenerate device402_2 are configured to receive a phase difference φ in microwave drives(pump signal 1 and pump signal 2).

At block 1804, a first input/output port (port 1) is coupled to thefirst port a1 and the another first port a2. At block 1806, a secondinput/output port (port 2) is coupled to the first port a1 and theanother first port a2, where communication between (signals (h) in onedirection and/or the opposite direction) the first input/output port(port 1) and the second input/output port (port 2) is based on the phasedifference φ between the pump drives feeding the three-wave mixers ofthe device 400.

The phase difference φ in the microwave drives is between a firstmicrowave drive (pump signal 1) and a second microwave drive (pumpsignal 2). The first and second input/output ports (ports 1 and 2) arepart of a hybrid coupler 404. A function of the first port a1 and theanother first port a2 are configured to be analogous. In other words,the function and connection of ports a1 and a2 are identical or nearlyidentical in the three-wave mixers 402_1 and 402_2 respectively.

A variable phase shifter 604 is coupled to either the firstnondegenerate device 402_1 or the second nondegenerate device 402_2. Thevariable phase shifter 604 is configured to determine/create the phasedifference φ in the microwave drives.

The phase difference φ is configured to determine/control that the firstinput/output port (port 1) and the second input/output port (port 2) arein transmission mode. The phase difference φ is configured todetermine/control that the first input/output port (port 1) and thesecond input/output port (port 2) are in reflection mode.

The phase difference between the microwave drives is configured todetermine a variable transmission-reflection (between ports 1 and 2).The variable transmission-reflection is such that a transmission (suchas a transmitting a signal at f₁) from the first input/output port (port1) to the second input/output port (port 2) or vice versa is configuredsuch that the transmission amplitude T for the signals varies between 0and 1 and the reflection parameter R varies between 0 and 1. Where thereflection parameter of the whole device S₁₁ and S₂₂ and thetransmission parameter of the whole device S₁₂ and S₂₁ satisfy therelations |S₁₁|=|S₂₂|=R, |S₁₂|=|S₂₁|=T, and R²+T²=1. Also, both R and Tdepend on the phase difference φ.

The first and second nondegenerate devices 402_1 and 402_2 arenondegenerate three-wave mixers in frequency conversion mode.

FIG. 19 depicts a flow chart 1900 of a method of forming/configuring amicrowave switch 400 according to embodiments of the present invention.At block 1902, a first Josephson parametric converter 402_1 includes aSignal port a1 and an Idler port b2 and a second Josephson parametricconverter 402_2 includes another Signal port a1 and another Idler portb2. At block 1904, the Signal port b1 is coupled to the another Signalport b2, where the first and second Josephson parametric converters areconfigured to receive a phase difference φ in microwave drives (pumpsignal 1 and pump signal 2). At block 1906, a first input/output port(port 1) and a second input/output port (port 2) are coupled to theSignal port a1 and the another Signal port a2, such that communication(e.g., signals at frequency f₁) between the first and secondinput/output ports (ports 1 and 2) is based on the phase difference.

The first Josephson parametric converter 402_1 includes a Signalresonator (e.g., resonator_a 1502) coupled to the Signal port a1 and thesecond Josephson parametric converter 402_2 includes another Signalresonator (e.g., resonator_a 1502) coupled to the another Signal porta2. The first Josephson parametric converter 402_1 includes an Idlerresonator (e.g., resonator_b 1504) coupled to the Idler port b1 and thesecond Josephson parametric converter 402_2 includes another Idlerresonator (e.g., resonator_b 1504) coupled to the another Idler port b2.One leg of a hybrid coupler 404 is coupled to the Signal port a1 andanother leg of the hybrid coupler 404 is coupled to the another Signalport a2.

FIG. 20 depicts a flow chart 2000 of a method of operating a microwaveswitch 400 according to embodiments of the present invention. At block2002, the microwave switch 400 receives a signal (f₁) at one of a firstinput/output port (port 1) and a second input/output port (port 2). Atblock 2004, the microwave switch 400 receives pump signals (pump signals1 and 2) having a phase difference φ. At block 2006, communication (fromport 1 to 2 and/or port 2 to 1) of the signal between the firstinput/output port (port 1) and the second input/output port (port 2) iscontrolled based on the phase difference.

Various embodiments of the present invention are described herein withreference to the related drawings. Alternative embodiments can bedevised without departing from the scope of this invention. Althoughvarious connections and positional relationships (e.g., over, below,adjacent, etc.) are set forth between elements in the followingdescription and in the drawings, persons skilled in the art willrecognize that many of the positional relationships described herein areorientation-independent when the described functionality is maintainedeven though the orientation is changed. These connections and/orpositional relationships, unless specified otherwise, can be direct orindirect, and the present invention is not intended to be limiting inthis respect. Accordingly, a coupling of entities can refer to either adirect or an indirect coupling, and a positional relationship betweenentities can be a direct or indirect positional relationship. As anexample of an indirect positional relationship, references in thepresent description to forming layer “A” over layer “B” includesituations in which one or more intermediate layers (e.g., layer “C”) isbetween layer “A” and layer “B” as long as the relevant characteristicsand functionalities of layer “A” and layer “B” are not substantiallychanged by the intermediate layer(s).

The following definitions and abbreviations are to be used for theinterpretation of the claims and the specification. As used herein, theterms “comprises,” “comprising,” “includes,” “including,” “has,”“having,” “contains” or “containing,” or any other variation thereof,are intended to cover a non-exclusive inclusion. For example, acomposition, a mixture, process, method, article, or apparatus thatcomprises a list of elements is not necessarily limited to only thoseelements but can include other elements not expressly listed or inherentto such composition, mixture, process, method, article, or apparatus.

Additionally, the term “exemplary” is used herein to mean “serving as anexample, instance or illustration.” Any embodiment or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs. The terms “at least one”and “one or more” are understood to include any integer number greaterthan or equal to one, i.e. one, two, three, four, etc. The terms “aplurality” are understood to include any integer number greater than orequal to two, i.e. two, three, four, five, etc. The term “connection”can include an indirect “connection” and a direct “connection.”

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedcan include a particular feature, structure, or characteristic, butevery embodiment may or may not include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

The terms “about,” “substantially,” “approximately,” and variationsthereof, are intended to include the degree of error associated withmeasurement of the particular quantity based upon the equipmentavailable at the time of filing the application. For example, “about”can include a range of ±8% or 5%, or 2% of a given value.

As previously noted herein, for the sake of brevity, conventionaltechniques related to superconducting device and integrated circuit (IC)fabrication may or may not be described in detail herein. By way ofbackground, however, a more general description of the superconductingdevice fabrication processes that can be utilized in implementing one ormore embodiments of the present invention will now be provided. Althoughspecific fabrication operations used in implementing one or moreembodiments of the present invention can be individually known, thedescribed combination of operations and/or resulting structures of thepresent invention are unique. Thus, the unique combination of theoperations described in connection with the fabrication of asemiconductor device according to the present invention utilize avariety of individually known physical and chemical processes performedon a superconducting over a dielectric (e.g., silicon) substrate, someof which are described in the immediately following paragraphs.

In general, the various processes used to form a micro-chip that will bepackaged into an IC fall into general categories, including, filmdeposition, removal/etching, and patterning/lithography. Deposition isany process that grows, coats, or otherwise transfers a material ontothe wafer. Available technologies include physical vapor deposition(PVD), chemical vapor deposition (CVD), electrochemical deposition(ECD), molecular beam epitaxy (MBE) and more recently, atomic layerdeposition (ALD) among others. Removal/etching is any process thatremoves material from the wafer. Examples include etch processes (eitherwet or dry), and chemical-mechanical planarization (CMP), and the like.Films of both conductors (e.g., poly-silicon, aluminum, copper, etc.)and insulators (e.g., various forms of silicon dioxide, silicon nitride,etc.) are used to connect and isolate components. Lithography is theformation of three-dimensional relief images or patterns on thesemiconductor substrate for subsequent transfer of the pattern to thesubstrate. In lithography, the patterns are formed by a light sensitivepolymer called a photo-resist. To build the complex structures of acircuit, lithography and etch pattern transfer steps are repeatedmultiple times. Each pattern being printed on the wafer is aligned tothe previously formed patterns and slowly the conductors, insulators andother regions are built up to form the final device.

The flowchart and block diagrams in the Figures illustrate possibleimplementations of fabrication and/or operation methods according tovarious embodiments of the present invention. Variousfunctions/operations of the method are represented in the flow diagramby blocks. In some alternative implementations, the functions noted inthe blocks can occur out of the order noted in the Figures. For example,two blocks shown in succession can, in fact, be executed substantiallyconcurrently, or the blocks can sometimes be executed in the reverseorder, depending upon the functionality involved.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdescribed herein.

What is claimed is:
 1. A microwave switch comprising: a firstnondegenerate device comprising a first port and a second port; a secondnondegenerate device comprising another first port and another secondport, the second port being coupled to the another second port, whereinthe first nondegenerate device and the second nondegenerate device areconfigured to receive a phase difference in microwave drives; a firstinput/output port coupled to the first port and the another first port;and a second input/output port coupled to the first port and the anotherfirst port, wherein communication between the first input/output portand the second input/output port is based on the phase difference. 2.The microwave switch of claim 1, wherein the phase difference in themicrowave drives is between a first microwave drive and a secondmicrowave drive.
 3. The microwave switch of claim 1, wherein: the firstand second input/output ports are part of a hybrid coupler; and afunction of the first port and the another first port are configured tobe equivalent in the first nondegenerate device and the secondnondegenerate device respectively.
 4. The microwave switch of claim 1,wherein a variable phase shifter is coupled to the first nondegeneratedevice or the second nondegenerate device.
 5. The microwave switch ofclaim 4, wherein the variable phase shifter is configured to determinethe phase difference in the microwave drives.
 6. The microwave switch ofclaim 1, wherein the phase difference is configured to determine thatthe first input/output port and the second input/output port are intransmission mode.
 7. The microwave switch of claim 1, wherein the phasedifference is configured to determine that the first input/output portand the second input/output port are in reflection mode.
 8. Themicrowave switch of claim 1, wherein the phase difference between themicrowave drives is configured to determine a variabletransmission-reflection mode.
 9. The microwave switch of claim 1,wherein the first and second nondegenerate devices are nondegeneratethree-wave mixers operated in frequency conversion mode.
 10. A method ofconfiguring a microwave switch comprising: providing a firstnondegenerate device comprising a first port and a second port and asecond nondegenerate device comprising another first port and anothersecond port, the second port being coupled to the another second port,wherein the first nondegenerate device and the second nondegeneratedevice are configured to receive a phase difference in microwave drives;coupling a first input/output port to the first port and the anotherfirst port; and coupling a second input/output port to the first portand the another first port, wherein communication between the firstinput/output port and the second input/output port is based on the phasedifference.
 11. The method of claim 10, wherein the phase difference inthe microwave drives is between a first microwave drive and a secondmicrowave drive.
 12. The method of claim 10, wherein: the first andsecond input/output ports are part of a hybrid coupler; and a functionof the first port and the another first port are configured to beequivalent in the first nondegenerate device and the secondnondegenerate device respectively.
 13. The method of claim 10, wherein avariable phase shifter is coupled to the first nondegenerate device orthe second nondegenerate device.
 14. The method of claim 13, wherein thevariable phase shifter is configured to determine the phase differencein the microwave drives.
 15. The method of claim 10, wherein the phasedifference is configured to determine that the first input/output portand the second input/output port are in transmission mode.
 16. Themethod of claim 10, wherein the phase difference is configured todetermine that the first input/output port and the second input/outputport are in reflection mode.
 17. The method of claim 10, wherein thephase difference between the microwave drives is configured to determinea variable transmission-reflection mode.
 18. The microwave switch ofclaim 10, wherein the first and second nondegenerate devices arenondegenerate three-wave mixers operated in frequency conversion mode.19. A microwave switch comprising: a first Josephson parametricconverter comprising a Signal port and an Idler port; a second Josephsonparametric converter comprising another Signal port and another Idlerport, the Signal port and the another Signal port being coupledtogether, wherein the first and second Josephson parametric convertersare configured to receive a phase difference in microwave drives; and afirst input/output port and a second input/output port coupled to theSignal port and the another Signal port, such that communication betweenthe Signal and another Signal ports is based on the phase difference.20. The microwave switch of claim 19, wherein the first Josephsonparametric converter comprises a Signal resonator coupled to the Signalport and the second Josephson parametric converter comprises anotherSignal resonator coupled to the another Signal port.
 21. The microwaveswitch of claim 19, wherein the first Josephson parametric convertercomprises an Idler resonator coupled to the Idler port and the secondJosephson parametric converter comprises another Idler resonator coupledto the another Idler port.
 22. The microwave switch of claim 19, whereinone leg of a hybrid coupler is coupled to the Signal port and anotherleg of the hybrid coupler is coupled to the another Signal port.
 23. Amethod of configuring a microwave switch comprising: providing a firstJosephson parametric converter comprising a Signal port and an Idlerport and a second Josephson parametric converter comprising anotherSignal port and another Idler port; coupling the Signal port to theanother Signal port, wherein the first and second Josephson parametricconverters are configured to receive a phase difference in microwavedrives; and coupling a first input/output port and a second input/outputport to the Signal port and the another Signal port, such thatcommunication between the first and second input/output ports is basedon the phase difference.
 24. The microwave switch of claim 23, whereinthe first Josephson parametric converter comprises a Signal resonatorcoupled to the Signal port and the second Josephson parametric convertercomprises another Signal resonator coupled to the another Signal port.25. A method of operating a microwave switch, the method comprising:receiving, by the microwave switch, a signal at one of a firstinput/output port and a second input/output port; receiving, by themicrowave switch, pump signals having a phase difference; andcontrolling communication of the signal between the first input/outputport and the second input/output port based on the phase difference.